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Blind cosmos

Out of a whole packet of cosmos (Sensation Mixed) I planted this year at least 50 per cent turned out to be blind, i.e. no flowers. This was embarrassing as I sell plants through my WI and on our stall at the village fete. I contacted the seed manufacturer (Mr Fothergill's) but all I got was the offer of another packet (no thanks) and the excuse that there were many reasons why a plant fails to flower. But 50 per cent seems a high ratio to me. The seeds were sown March/April in plugs in a greenhouse, potted on and grew into healthy looking plants. The blind ones are very tall and healthy. Have other gardeners had this problem with cosmos. 


  • Lots of people seem to have been complaining about non-flowering Cosmos this year. Some of ours have been the same - very healthy looking plants but few or no flowers. I think 'blind' is the wrong term though - given time the plants should flower very well, but with the weather getting colder they'll probably just run out of time. I doubt there's anything wrong with the seed - more that the weather this year has favoured vegetative growth over flowering.

  • punkdocpunkdoc Posts: 14,632

    Cosmos are long night flowers and therefore are not really meant to do well in the UK. Below is an extract from a paper written on the subject

    What are short day and long day plants?Asters provide color late in the fall, when many flowers arefading into memory.February 19, 2003

    To understand plant flowering, you need to get a handle on "photoperiodism," or amount of light and darkness a plant is exposed to. The amount of uninterrupted darkness is what determines the formation of flowers on most types of plants, explained Ann Marie VanDerZanden, horticulturist with the Oregon State University Extension Service.

    Botanists used to think that the length of daylight a plant was exposed to determined whether a plant would form flowers. But experiments proved otherwise. It is the length of darkness that a plant experiences that plays the most crucial role.

    A plant that requires a long period of darkness, is termed a "short day" (long night) plant. Short-day plants form flowers only when day length is less than about 12 hours. Many spring and fall flowering plants are short day plants, including chrysanthemums, poinsettias and Christmas cactus. If these are exposed to more than 12 hours of light per day, bloom formation does not occur.

    Other plants require only a short night to flower. These are termed "long day" plants. These bloom only when they receive more than 12 hours of light. Many of our summer blooming flowers and garden vegetables are long day plants, such as asters, coneflowers, California poppies, lettuce, spinach and potatoes. These all bloom when the days are long, during our temperate summers.

    And some plants form flowers regardless of day length. Botanists call these "day neutral" plants. Tomatoes, corn, cucumbers and some strawberries are day-neutral. Some plants, such as petunias defy categorization, said VanDerZanden.

    "They flower regardless of day length, but flower earlier and more profusely with long days," she said.

    Horticulturists and home gardeners manipulate the day and night length (indoors with lights) to get plants to bloom at times other than they would naturally.

    For example, chrysanthemums, short day plants, naturally set flower and bloom with the long nights of spring or fall. But by making the days shorter by covering the chrysanthemums for at least 12 hours a day for several weeks over the late spring and early summer, you can simulate the light and darkness pattern of spring or fall, thereby stimulating summer blooming.

    Or you can bring a long-day plant into bud formation and eventual bloom early before our day lengths surpass 12 hours. Put the plant under grow lights for a few hours a day beyond natural daylength for a few weeks. Adding supplemental day length to stimulate early blooming is a common practice in the nursery and fresh flower industry, especially this time of year, for Valentine's Day and Easter flowers.

    How can you lie there and think of England
    When you don't even know who's in the team

    S.Yorkshire/Derbyshire border
  • This is not the first year this has happened, it happened last year but not to the extent of this year's failure. Don't recall it happening in years previous to 2015. Odd.

  • LynLyn Posts: 23,087

    They won't flower in rich soil, maybe you fed your garden with something stronger this year? 

    They flower best in poor soil, I had the same problem. I grow them in containers now with multi purpose compose and no extra feed. 

    Gardening on the wild, windy west side of Dartmoor. 

  • GrajeanGrajean Posts: 434

    Mine are finally flowering and have lots of buds, masses of growth so perhaps a late display hopefully.

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